cmd/internal/obj: eliminate LSym.Version

cmd/internal/obj: eliminate LSym.Version

There were only two versions, 0 and 1,
and the only user of version 1 was the assembler,
to indicate that a symbol was static.

Rename LSym.Version to Static,
and add it to LSym.Attributes.
Simplify call-sites.

Passes toolstash-check.

Change-Id: Iabd39918f5019cce78f381d13f0481ae09f3871f
Reviewed-on: https://go-review.googlesource.com/41201
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>